Eio_mock.HandlerSourceControl how a mock responds.
This module is mostly useful when writing custom mocks. Individual mocks usually provide convenience wrappers around this.
A handler that provides values of type 'a.
make default_action is a new handler that initially always runs default_action.
set_handler t fn sets (replaces) the function to be called whenever the handler is run.
seq t actions sets a handler function that performs the next action in actions on each call. When there are no more actions, it runs the default handler.